1. Field of the Invention
This invention relates to a system for controlling and feeding electrical power to heaters for long fluid-flow pipes. More specifically, the present invention provides a system for controlling and feeding electrical power to an internal wire impedance system for heating long flow lines.
2. DESCRIPTION OF THE PRIOR ART
Long-distance pipelines often require the fluid flowing in them to have lower viscosities than they would have at ambient temperature of the pipe. In order to reduce the viscosity of the fluid, heat is generally transferred into the fluid. A way to achieve this is through steam tracing, that is, a system which uses steam flowing in a separate conduit adjacent to the one transporting the fluid. Another system is one using alternating current and the effects of a magnetic field produced by it to increase the temperature of the fluid in the flow pipe. This second method has in the past been called "skin effect heating," or more correctly, "internal wire impedance heating."
Industrial practice has used the skin effect or internal wire impedance heating which, under current practice, uses a ferromagnetic pipe attached substantially parallel and either interior or exterior to a fluid-flow pipe. The ferromagnetic pipe has longitudinally extending through it an insulated copper wire in series with both an alternating current (AC) source of power and the ferromagnetic pipe. A theoretical explanation of the operation is that electric current flows through the insulated wire and returns back on the inside wall of the ferromagnetic pipe due to the skin effect, with no current flowing on the outside wall.
In prior installations of this system which I am aware of, single-point power connections to the internal insulated wire are used. The arrangement necessitates the use of high-voltage switch gear as well as high-voltage insulation on the internal insulated wire. Additionally, for the high voltages required to heat a relatively long pipeline, specially designed high-voltage transformers are required, resulting in high costs and long waits for delivery of such special equipment.
The present invention includes an arrangement which permits the use of readily available and less costly standard equipment.